He doesn't need to take responsibility for the protesters at his rallies, that's on them.
However...................how those protesters are treated by his supporters and campaign workers IS partially his responsibility. Instead of saying punch them in the face, carry them out on a stretcher, or volunteering to pay for the legal bills of people who get violent, he should have stayed with get them out.
Face it, almost EVERY person running for office will face protesters at some time, some will face them on a regular basis.
How you handle the protesters says a lot about how you'd run the country.